1. Field of the Invention
The present invention is related to a method and related device for detecting signals in a TMDS transmission system, and more particularly, to a method and related device capable of correctly determining an operating state of a transmitter in the TMDS transmission system.
2. Description of the Prior Art
With the advancement of multimedia technology, people demand more and more digital video products, such as next generation video game consoles, digital TVs, DVD players, and etc. In order to transmit digital video data, the industry advanced a high definition multimedia interface (HDMI), which is developed from a digital visual interface (DVI). The HDMI utilizes a transition minimized differential signaling (TMDS) method for coding signals to transmit high definition video signals and multi-channel audio signals.
Please refer to FIG. 1, which is a schematic diagram of a TMDS transmission system 10 of the prior art. The TMDS transmission system 10 includes a transmitter TX, a receiver RX and channels TMDS_CH0 to TMDS_CH3. In the TMDS transmission system 10, the channels TMDS_CH0 to TMDS_CH2 are utilized for transmitting video and audio signals, and the channel TMDS_CH3 is for clock signals.
Please continue to refer to FIG. 2, which is a schematic diagram of an arbitrary channel TMDS_CHx of the channels TMDS_CH0 to TMDS_CH3 in FIG. 1. As illustrated in FIG. 2, the channel TMDS_CHx is composed of a first differential line L1 and a second differential line L2. The receiver RX part of the channel TMDS_CHx (right half of FIG. 2) comprises a detection circuit 200 and resistors 202, 204, and the transmitter TX part thereof (left half of FIG. 2) comprises a current source 206 and switches 102, 104. The detection circuit 200 utilizes an edge detection method to analyze voltage waveforms of the first differential line L1 and the second differential line L2, so as to determine whether the transmitter TX transmits data via the channel TMDS_CHx, such that the receiver RX can accordingly determine whether to start receiving signals or remain in standby.
In FIG. 2, currents ITX1, ITX2 passing through the current source 206 are completely provided by the receiver RX. However, due to limitations caused by HDMI specifications, if the receiver RX detects an operating state of the transmitter TX while the transmitter TX is operating in a transmitting state, the receiver RX will be forced to supply the currents ITX1, ITX2. Under such condition, in order to more efficiently utilize current resources of the receiver RX, the prior art must reduce a detection current IRX provided by the receiver RX when the receiver RX detects the operating state of the transmitter TX. However, loadings of the receiver RX are composed of two passive elements—resistors 202, 204—which cannot actively control the current passing through themselves. Thus, the current resources of the receiver RX are still dominated by the transmitter, so that the detection current IRX cannot be effectively reduced.